1. Field of the Invention
The present invention relates to a fuel injection control device for controlling an amount of fuel to be injected at acceleration in an internal combustion engine.
2. Description of the Prior Art
In an electronically controlled fuel injection device for controlling the amount of fuel to be injected from a fuel injector according to an operational condition of the internal combustion engine, computation of the amount of fuel to be injected and control of injection are generally carried out according to a crank angle signal generated synchronously with the rotation of the crank shaft. That is to say, the fuel injection amount meeting an output power to be required by the engine is computed according to an amount of suction air and a rotational speed of the engine, etc. with a period of 360.degree. of a crank angle (360.degree. CA) synchronously with the rotation of the crank shaft. Just after the computation, fuel injection (synchronous injection) is carried out at a predetermined timing synchronous with a signal of the crank angle 360.degree. CA.
Conventionally, in some type of engines when an increased amount of fuel is required at acceleration, for example, the fuel is injected at a timing different from that of the synchronous injection as synchronous with a crank angle position, which is so-called asynchronous injection.
As to control of the asynchronous injection at acceleration, there is described in Japanese Laid-open Patent Publication No. 59-90768 for example that a displacement speed of a throttle valve is computed, and if the result of computation is equal to or more than a fixed value, the asynchronous injection is carried out just after the computation.
However, since the conventional fuel injection control device is designed to carry out the asynchronous fuel injection according to the amount of change in the throttle valve angle every short fixed time, a noise enters a signal of the throttle valve angle to generate an erroneous asynchronous injection signal, resulting in malfunction of the fuel injector.
Further, in case of acceleration from a running operation at a large throttle valve angle, a change in suction air amount with respect to a change in the throttle valve angle is actually relatively small as compared with acceleration from a low-load operational range. However, an excessively increased amount of fuel is sometimes injected according to erroneous asynchronous injection signals to cause overrichness of fuel.
In the case that the engine rotational speed is within a high-speed rotational range, the synchronous injection is carried out with a high density and no asynchronous injection is generally required even at acceleration from the high-speed rotational range. However, the asynchronous injection is actually sometimes carried out to result in an undue increase in fuel.